With this type of conventional technique, a traveling machine includes an excavator device attached to a front portion of a swiveling deck mounted to be swivellable about a vertical axis, an operating deck fixed on the swiveling deck, a driver's seat mounted on the operating deck, an engine mounted to a rear portion of the swiveling deck, an operational oil tank mounted to a right side portion of the swiveling deck, and right and left controlling devices disposed on the right and left sides of the driver's seat. The right and left controlling devices include a main control valve operated by a control lever to allow such operations as a swiveling operation of the swivel deck, operations of a boom, an arm and a bucket of the excavator device, etc. (See JP2002-149255A).